High Density Lithium Cobalt Oxide for Rechargeable Batteries

ABSTRACT

The disclosure relates to positive electrode material used for Li-ion batteries, a precursor and process used for preparing such materials, and Li-ion battery using such material in its positive electrode. The disclosure describes a higher density LiCoO 2  positive electrode material for lithium secondary batteries, with a specific surface area (BET) below 0.2 m 2 /g, and a volumetric median particle size (d50) of more than 15 μm. This product has, improved specific capacity and rate-capability. Other embodiments of the disclosure are an aggregated Co (OH) 2 , which is used as a precursor, the electrode mix and the battery manufactured using abovementioned LiCoO 2 .

The invention relates to positive electrode material used for Li-ionbatteries, a precursor and process used for preparing such materials,and Li-ion battery using such material in its positive electrode.

Compared to Ni—Cd and Ni—MH rechargeable batteries, Li-ion batteriesboast an enhanced energy density, mainly due to their higher 3.6 Vworking voltage. Since their commercialization in 1991 by SONY, Li-ionbatteries have seen their volumetric energy density increasecontinuously. In 1995, the capacity of a typical 18650 cylindrical cellwas about 1.3 Ah. In 2006, the capacity of the same type of cell isabout 2.6 Ah. Such a high energy density has enabled a wide range ofapplications. Li-ion batteries have become the dominant secondarybattery for portable application, representing a market share of about70% in 2006.

Such significant increase of energy density of Li-ion batteries has beeninitially realized by optimizing cell design, accommodating more activeelectrode materials in a fixed volume cell. Later efforts concentratedon improving the energy density of the electrodes. Using a high densityactive electrode material is one way to achieve this goal. As LiCoO₂still continues to be used as positive electrode material for themajority of commercial Li-ion batteries, a highly dense variety of thismaterial is in demand.

The tap density of electrode materials is usually a good indicator ofelectrode density. However, in some cases, a high tap density does notguarantee a high electrode density. For example, as demonstrated by Yinget al. (Journal of power Sources, 2004) or in CN1206758C, the tapdensity of a LiCoO₂ powder with large secondary spherical particle size,but small primary size, can be as high as 2.8 g/cm³. However, because ofits small primary particle size, and possibly because of voids in thesecondary particles, the obtained electrode density is notcorrespondingly high. For this reason, density of electrode materialsshould preferably be measured under a pressure similar to the industrialconditions prevailing during actual electrode manufacture, instead of bytapping. In this invention, density therefore refers to press density,and not to tap density.

The theoretical density of LiCoO₂ is about 5.1 g/cm³. For actual LiCoO₂powders, factors that impact the density are a.o. the shape ofparticles, the size of primary particles and the particle sizedistribution. In today's industry, the medium primary particle size ofLiCoO₂ used for different application is in the range of 1 to 20 μm.Generally, the larger the median primary particle size (d50), the higheris the press density. In addition, as proposed in CN1848491A, electrodedensity can be increased further by mixing larger LiCoO₂ particles with15 to 40 wt % of finer particles.

Besides density reasons, a large median primary particle size is alsodesirable for safety purposes, especially for large cells such as the18650 model cylindrical cells that are used in laptop computer. Duringcharge, lithium atoms in LiCoO₂ are partially removed. LiCoO₂ becomesLi_(1-x)CoO₂ with x>0. At high temperatures caused by certain abusecondition, Li_(1-x)CoO₂ tends to decompose and then to release O₂. Thereleased O₂ easily reacts with organic solvent in the batteryelectrolyte, resulting in fire or explosion of the battery. Using LiCoO₂with a large median primary particle size and low specific surface area(BET) reduces these risks, as pointed out by Jiang J. et al.(Electrochimica Acta, 2004).

Therefore, for both safety and energy density reasons, LiCoO₂ with largemedian primary particle size, such as 15 μm or above, is preferred, inparticular for large Li-ion cells. Materials with a large mass medianprimary particle size (d50) have also a relatively low BET. A d50 largerthan 15 μm typically leads to a BET below 0.2 m²/g.

In a usual manufacture process of LiCoO₂, powderous Co₃O₄ and Li₂CO₃ aremixed and then fired at a temperature ranging from 800° C. to 1100° C.The d50 of the Co₃O₄ needs to be relatively small, usually below 5 μm,to ensure a sufficient reactivity. The growth of the LiCoO₂ particles iscontrolled by the firing temperature and time, and by the amount ofexcess Li (added as Li₂CO₃). To make LiCoO₂ with a d50 larger than 15μm, at least 6 at. % of excess Li per Co atom is needed, as this excessfavours crystal growth. However, part of the excess Li also enters theLiCoO₂ structure. Therefore, the final product will be Liover-stoichiometric. This is why all current LiCoO₂ material with largeprimary particle size (or a low BET, which is equivalent) issignificantly over-stoichiometric. Due to this excess Li in theirstructure, such materials have a lower capacity because some active Co³⁺has been replaced by inactive Li⁺. In this respect, it should be notedthat in this application, LiCoO₂ is used to designate a wide variety oflithium cobalt oxides having stoichiometries that may slightly deviatefrom the theoretical.

One example of this process can be found in EP 1 281 673 A1. Here acomposition Li Co_((i-x)) Mg_(x)O₂ is disclosed, wherein x is 0.001 to0.15, and having an average particle diameter of 1.0 to 20 μm and a BETof 0.1 to 1.6 m²/g. However, the examples clearly show that the inventordid not succeed in manufacturing a lithium cobalt (magnesium) oxidepowder having both of: a d50 of more than 15 μm, and a specific surfacearea (BET) of less than 0.2 m²/g. The maximum d50 achieved in thisdocument is 8.3 μm in a comparative example.

It is finally also desirable for electrode materials to provide goodrate capability. Rate capability is defined as the ratio of specificdischarge capacity at a higher discharge rate (typically 2 C), to thespecific discharge capacity at a lower rate (typically 0.1 C).Unfortunately, current LiCoO₂ with large primary particle size showsrelatively poor rate capability, as shown in JP3394364 and by ChenYan-bin et al. (Guangdong Youse Jinshu Xuebao, 2005). Such poor ratecapability is considered to be related to the longer Li diffusion pathfor material with larger primary particle size when Li is removed orreinserted during charge or discharge.

In summary, LiCoO₂ with a large primary particle size is preferred forLi-ion battery for improved safety and energy density. However, currentlarge particle size powders show sub-optimal capacity and ratecapability because of the significant Li-excess in their structure.

A first principal objective of this invention is therefore to provide arelatively coarse-grained electrochemically active LiCoO₂ powder,without significant Li-excess.

The first active product embodiment of the invention concerns a lithiumcobalt oxide powder for use as an active positive electrode material inlithium-ion batteries, having a d50 of more than 15 μm, a BET of lessthan 0.2 m²/g, and a Li to Co atomic ratio between 0.980 and 1.010,preferably of less than 1.000, more preferably of less than 0.999. Thementioned particle size is evidently a primary particle size, and theparticles are neither agglomerated or coagulated, nor aggregated.

This Li to Co ratio range is chosen so that such composition gives adischarge capacity of more than 144 mAh/g at 2 C, and rate capability(Q2 C/Q0.1 C) of more than 91%. For product with an Li to Co ratio lowerthan 0.980, electrochemically inactive and thus undesired Co₃O₄ has beenidentified with X-ray diffraction.

It should be mentioned that in US 2002/119371 A1 an electrochemicallyactive material is used, having the formula of a ternary (Li-Me1-O) orquaternary (Li-Me1-Me2-O) lithium transition metal oxides, wherein Me1and Me2 are selected from the group consisting of Ti, V, Cr, Fe, Mn, Ni,Co. It can further comprise up to about 15 atom percent of Mg, Al, N orF to stabilize the structure, and have a BET of 0.1-2 m²/g and aparticle size of from about 1 to about 50 μm. However, the ratio Li/Cois said to be in the wide range of 0.98 to about 1.05, without giving amore specific example.

Also, in EP 1 052 716 A2 a Li-transition metal composite oxideLi_(A)M_((1-x))Me_(x)O₂ is disclosed, with M being Co, Ni, Mn, V, Ge andthe like, and preferably LiCoO₂, where A is 0.05-1.5, preferably0.1-1.1, and x can be zero. This composite oxide preferably has anaverage paricle size of 10-25 μm, and also preferably has a BET of0.1-0.3 m²/g. In the examples (Table 1) however, the combination ofaverage particle size above 15 μm and BET under 0.2 m²/g is notdisclosed together with a Li/Co atomic ratio between 0.980 and 1.010.

The second active product embodiment of the invention concerns a lithiumcobalt oxide powder for use as an active positive electrode material inlithium-ion batteries, having a d50 of more than 15 μm, a BET of lessthan 0.2 m²/g, and with an OH⁻ content between 0.010 and 0.015 wt % morepreferably between 0.0125 and 0.015.

This OH⁻ range was found to correspond to the nearly stoichiometricproducts delivering the optimal electrochemical performances. By OH⁻content is meant the OH⁻ as determined by acid-base titration of anaqueous dispersion of the lithium cobalt oxide powder. Titration isperformed using a 0.1 M HCl solution. As some carbonates could bepresent, the relevant amount of acid is calculated as the amount of acidto reach pH 7, minus the amount of acid to reach pH 4 from pH 7.

It should be mentioned here that in US 2006/263690 A1 a positiveelectrode material

Li_(p)Co_(x)M_(y)O_(z)F_(a) is claimed, where 0.9≦p≦1.1, y and a may bezero (and x=1), 1.9≦z≦2.1. D50 is from 5 to 15 μm (although also up to20 μm is mentioned singularly), and BET from 0.3 to 0.7 m²/g. Thislithium composite oxide has a remaining alkali amout of at most 0.02,and preferably at most 0.01 wt %. All of the examples show a combinationof a BET value over 0.2 m²/g, and a D50 under 15 μm.

In WO99/49528 (equivalent to EP 1 069 633 A1) on the other hand, aLiCoO2 is disclosed which comprises a mixture of primary particles ofsmall crystals having a Feret's diameter in a projection drawing by SEMobservation in a range from 0.4 to 10 μm and an average diameter of 5 μmor less, and secondary particles formed by ‘gathering’ of the primaryparticles and having a diameter of 4 to 30 μm, wherein the mole ratio ofCo to Li is 0.97 to 1.03, and at least a part of small crystalsconstituting the secondary particles are joint by the junction throughsintering, and the secondary particles are in the shape of a circle oran ellipse. This material is preferably obtained by mixing a lithiumsalt and a cobalt source where cobalt oxyhydroxide (CoOOH) is used as araw material and comprises secondary particles falling in the range of 4to 30 μm and formed by gathering of a number of primary particles of 0.2to 0.8 μm and subsequently, by carrying out a heat treating on thismixture.

The characteristics of both the first and second embodiments of theinvention mentioned before can advantageously be combined.

The above mentioned dependency of capacity and rate capability on the Lito Co ratio is also applicable to doped products, in particular forMg-doped LiCoO₂. A third active product embodiment is therefore alithium cobalt oxide powder for use as an active positive electrodematerial in lithium-ion batteries according to embodiments 1 and 2,further comprising Mg as doping elements with a Mg to Co atomic ratiobetween 0.001 to 0.05. However, in this case, it is the atomic ratio ofLi to the sum of Co and Mg (instead of to Co alone) that should bebetween 0.980 and 1.010, and be preferably less than 1.000, and morepreferably less than 0.999.

As described above, mixing relatively coarse lithium cobalt oxide powderwith finer powder can further increase the electrode density. Therefore,the fourth active product embodiment of this invention is defined apowder mixture for use as an active positive electrode material inlithium-ion batteries, comprising at least 50% by weight of a firstpowder according to any one of embodiments one to three, and comprisinga second powdered active component consisting of lithiumtransition-metal oxide. The said second powder should preferably befiner than said first powder, and, in particular result in a powdermixture showing a bimodal particle size distribution.

Such a bimodal powder mixture should preferably comprise anelectrochemically active second powder, consisting of lithium cobaltoxide, the mixture having a BET of less than 0.5 m²/g.

A second principal objective of this invention is to provide aneconomical precursor that can be used to manufacture the inventedproducts effectively and economically.

Usually, LiCoO₂ is made by solid state reaction of Co₃O₄ as a Co sourcewith Li₂CO₃ as a Li source.

As explained above, the customary use of Co₃O₄ as a precursor for LiCoO₂has been found to imply the addition of excess Li when large particlesizes are sought, this excess resulting in undesired side effects, suchas reduced capacity and rate capability. Moreover, and from the point ofview of process robustness, it appears that the mass median primaryparticle size (d50) of the LiCoO₂ product is very sensitive tovariations of the firing temperature and of the Li-excess. Indeed, a 10°C. variation in firing temperature causes a d50 change of 2 to 3 μm, anda 1% variation in Li causes a d50 change of 2 to 4 μm. Therefore, usingCo₃O₄, a very strict control of the Li to Co blending ratio and of thefiring temperature is required in order to obtain a consistent result.Such a control is difficult to ensure, in particular when production isenvisaged at an industrial scale.

This problem does not occur when using a specially prepared aggregatedCo(OH)₂ as a precursor. Moreover, Co₃O₄ is relatively expensive comparedto other alternatives such as Co(OH)₂. To reduce costs, Co(OH)₂ hastherefore already been proposed to replace Co₃O₄ as a cheaper Co source,as for example in JP2002321921. However, two firing steps are neededaccording to the described process. Due to the high costs of such adouble firing process, the total savings remain limited.

According to the inventors' results, the shape of the aggregated Co(OH)₂precursor particles can be preserved after firing with a Li precursor.The secondary particle size of the end product is only slightly smallerthan that of aggregated Co(OH)₂ precursor. The primary particle size ofLiCoO₂ still depends on the firing conditions, such as Li to Co ratio,firing temperature and firing time.

With the invented aggregated precursor, using a suitable blending ratioof Li to Co, and a single firing step, the primary particles in the endproduct grow larger, while there is little change in secondary particlesize. Under certain conditions, such as with a blending ratio of Li toCo between 1.04 and 1.06, and a firing temperature in the range of 960to 1020° C., the primary particles forming the secondary structure canindeed grow together. In this way, and by using aggregated Co(OH)₂, theproducts mentioned in the aforementioned embodiments can be preparedcost effectively.

A precursor product according to this invention is thus defined aseither one or more of an non-sintered agglomerated powderous cobaltoxide, hydroxide and oxy-hydroxide, having a secondary particle sizewith a d50 of more than 15 μm. Preferably the primary particles have aprimary particle size with a d50 of less than 5 μm. The secondaryparticles preferably have a spherical shape. The cobalt oxide can eitherbe Co₃O₄, Co₂O₃, or a partially oxidized and dried Co(OH)₂. It isimportant that the secondary particles of the precursor do not containany sintered primary particles, since the desired result can only beobtained using a single firing step.

A third principal objective of this invention concerns a process formanufacturing the invented active products, starting from the inventedprecursor products.

To this end, a process is defined whereby the Co precursor is mixed withLi source, according to a Li to Co ratio in the range between 1.04 and1.06, and firing the mixture with a single firing at temperature between960° C. and 1020° C. This single-firing process comprises the steps of:

-   -   providing for a precursor compound as described above,    -   mixing said precursor compound with a Li source according to a        Li to Co ratio R between 1.04 and 1.06, and    -   firing said mixture with a single firing at a temperature T        between 960° C. and 1020° C., whereby the quotient Q of the        firing temperature T and the Li to Co ratio R corresponds to        920≦Q≦965. When 1.04≦R≦1.05, then preferably 920≦Q≦960, and more        preferably 925≦Q≦945. When 1.05<R≦1.06, then preferably        925≦Q≦965, and more preferably 945≦Q≦960.

Another objective of the invention is to provide Li-ion batteries withincreased energy density and rate capability. With the product mentionedin the first embodiment, the capacity and rate capability of a cell withcertain volume can be increased. Therefore the energy density and ratecapability can be improved.

Finally, this invention also concerns Li-ion batteries that use theproduct mentioned in the abovementioned active product embodiments, aspositive electrode materials.

The following figures illustrate the invention.

FIG. 1: Discharge capacity and rate capability vs. the Li to Co ratiofor LiCoO₂ with a BET of 0.15 to 0.18 m²/g and a d50 of 15.7 to 18.2 μm.

FIG. 2: Discharge capacity and rate capability vs. OH⁻ content forLiCoO₂ with a BET of 0.15 to 0.18 m²/g and a d50 of 15.7 to 18.2 μm.

FIG. 3: XRD diffraction pattern of Example 1 (a) and Comparative Example2 (b).

FIG. 4: SEM image of the aggregated precursor used in Examples 1, 2, and3.

FIG. 5: SEM image of final product according to Example 1.

FIG. 6: SEM image of final product according to Comparative Example 3.

Products with similar medium particle size (in the range of 15.7 μmto18.2 μm) and similar BET (in the range of 0.15 m²/g to 0.18 m²/g) butwith various Li to Co ratios (in the range of 0.95 to 1.02) wereprepared. Particle size and specific surface area of all productsstudied were kept nearly constant. The Li diffusion path lengths for thedifferent products are therefore comparable. The variation in dischargecapacity (Q) at low rate (0.1 C) and at high rate (2 C) amongst theproducts therefore can be attributed to variation of the Li to Co ratio.According to electrochemical results, as shown in FIG. 1, products witha Li to Co ratio in the range of 0.980 to 1.010 offer optimalcharacteristics: a high capacity with only a limited decrease at highrate, corresponding to a rate capability (ratio of Q@0.1 C to Q@2 C) ofmore than 91%. With lower Li to Co ratios, products have less capacity,probably due to the appearance of inactive Co₃O₄ impurities. Forexample, a significant X-ray diffraction peak of Co₃O₄ was found in thediffraction pattern of a product with a ratio of 0.970. On the otherhand, products with too high Li to Co ratios lose some of theircharge-discharge capacity, probably because of the substitution ofactive Co³⁺ by inactive Li⁺.

FIG. 2 shows a similar correlation as a function of the OH⁻ content forthe same samples used in FIG. 1. The optimal OH⁻ range is 0.010 to 0.015wt %. As OH⁻ content increases, the rate capability initially increases.However, as it increases beyond 0.015 wt %, the rate capability sharplydegrades.

EXAMPLES

The present invention is described in more detail by examples andcomparative examples below. However, the examples are only illustrative,and, therefore, not intended to limit the scope of the presentinvention.

To prepare Co(OH)₂ or Mg-doped Co(OH)₂, a suitable Co²⁺ salt, preferablyCoSO₄.6H₂O, is dissolved in water. The so obtained solution typicallycontains about 55 g/L of Co. Co(OH)₂ is then precipitated by adding anaqueous base, preferably a solution of 25% NaOH, and a 260 g/L NH₃ tothe Co solution into a stirred and heated, preferably to 62° C.,overflow reactor tank. The reactor tank is typically filled with a seedslurry of Co(OH)₂ containing NaOH, Na₂SO₄, ammonia, and water. As thereaction proceeds, the resulting overflow slurry is collected, and apink solid is separated from the supernatant by filtration. Afterwashing with water, the solid is dried in a convection oven to aconstant mass. The resulting powder is a highly pure, spheroidal,flowable, oxidation resistant Co(OH)₂ that is easily screened andprocessed.

Mg-doped Co(OH)₂ is produced under similar conditions as the above pureCo(OH)₂. The only difference is that instead of using a feed solution ofpure CoSO₄, the feed solution is supplemented with a suitable Mg²⁺ salt,preferably MgSO₄.

During the precipitation reaction, pH (temperature uncompensated) ismaintained between 10.4 and 11.3, preferably between 10.8 and 11.0. Ingeneral, a higher pH will result in the precipitation of smallersecondary particles, while a lower pH will result in the precipitationof larger secondary particles. The resulting spherical Co(OH)₂ has d50particle size volume distribution values between 5 and 50 μm and spans(defined as (d90-d10)/d50) ranging from 0.5 to 2.0. More precisely, thesteady state production of Co(OH)₂ will result in D50 particle sizesranging from 14 to 21 μm with spans ranging from 0.9 to 1.2.Alternatively, a less spherical agglomerated Co(OH)₂ material can beproduced by increasing the pH. This material retains water more easilyand has steady state d50 particle sizes ranging from 4-14 μm with spanstypically greater than 1.0.

Particle size distribution of LiCoO₂ is measured using a MalvernMastersizer 2000. The median volumetric particle size is assumed to beequivalent to the median mass particle size represented by d50. Thespecific surface area of LiCoO₂ is measured with theBrunauer-Emmett-Teller (BET) method using a Micromeritics Tristar. Tomeasure the press density of LiCoO₂, a mixture is made with 95 wt %active material, 2.5 wt % carbon black, and 2.5 wt % polyvinylidenefluoride (PVDF) in N-methylpyrrolidone (NMP). After drying, 1.2 g powderis put in a SPEX 3613 13 mm die set and pressed under 3.7 metric ton percm². Press density is calculated by dividing the mass by the volume ofthe pressed pellet. The OH⁻ content of fired LiCoO₂ is measured by pHtitration in water with a 0.1 M HCl solution.

Electrochemical performance is tested in coin type cells, with a Li foilas counter electrode in a lithium tetrafluoroborate (LiBF₄) typeelectrolyte at 24° C. Cells are charged to 4.3 V and discharged to 3.0V. A specific capacity of 160 mAh/g is assumed for the determination ofthe discharge rates. For example, for discharge at 2 C, a specificcurrent of 320 mA/g is used.

Example 1

A mixture is made with aggregated Co(OH)₂ with a d50 of 19.3 μm andLi₂CO₃ with a Li to Co (atomic) blending ratio of 1.05. The mixed powderis fired in air at 980° C. for 12 hours. After cooling, the obtainedmaterial is milled and screened with a 270 mesh screen.

Example 2

Same as example 1, except that the firing temperature is 970° C.

Example 3

A mixture is made with aggregated Co(OH)₂ with a d50 of 19.3 μm andLi₂CO₃ with a Li to Co blending ratio of 1.04. The mixed powder is firedin air at 990° C. for 10 hours. After cooling, the obtained material ismilled and screened with a 270 mesh screen.

Example 4

A mixture is made with aggregated (Co_(0.99)Mg_(0.01))(OH)₂ with a d50of 18.7 μm, which is dried at 175° C. for 5 hours, and Li₂CO₃ with a Lito (Co_(0.99)Mg_(0.01)) blending ratio of 1.05. The mixed powder isfired in air at 980° C. for 12 hours. After cooling, the obtainedmaterial is milled and screened with a 270 mesh screen.

Example 5

Product from Example 3 is mixed with commercially available Cellcore® D5(Umicore, Belgium) in a 80 to 20 weight ratio. Cellcore® D5 has a d50 of6.5 μm, which is smaller than the product from Example 3 (17.4 μm). Thepress density of the mixed powder is 3.83 g/cm³, which is higher thanthat of Example 3 (3.79 g/cm³).

Comparative Example 1

A mixture is made with Co₃O₄ with a d50 of 3 μm and Li₂CO₃ with a Li toCo blending ratio of 1.065. The mixed powder is fired in air at 960° C.for 12 hours. After cooling, the obtained material is milled andscreened with a 270 mesh screen.

Comparative example 2

A mixture is made with aggregated Co(OH)₂ with a d50 of 19.3 μm andLi₂CO₃ with a Li to Co blending ratio of 1.035. The mixed powder isfired in air at 1020° C. for 10 hours. After cooling, the obtainedmaterial is milled and screened with a 270 mesh screen.

Comparative Example 3

A mixture is made with aggregated Co(OH)₂ with a d50 of 19.3 μm andLi₂CO₃ with a Li to Co blending ratio of only 1.005. The mixed powder isfired in air at 920° C. for 12 hours. After cooling, the obtainedmaterial is milled and screened with a 270 mesh screen.

Comparative Example 4

A mixture is made with aggregated Co(OH)₂ with a d50 of only 9 μm andLi₂CO₃ with a Li to Co blending ratio of 1.06. The mixed powder is firedin air at 960° C. for 12 hours. After cooling, the obtained material ismilled and screened with a 270 mesh screen.

Comparative Example 5

A mixture is made with Mg-doped Co₃O₄ (Co to Mg ratio of 99:1) with ad50 of 3 μm and Li₂CO₃ with a Li to Co blending ratio of 1.057. Themixed powder was fired in air at 960° C. for 15 hours. After cooling,the obtained material is milled and screened with a 270 mesh screen.

Comparative Example 6

A mixture is made with aggregated Co(OH)₂ with a d50 of 19.3 μm andLi₂CO₃ with a Li to Co blending ratio of 1.06. The mixed powder is firedin air at 960° C. for 12 hours. After cooling, the obtained material ismilled and screened with a 270 mesh screen.

Comparative Example 7

A mixture is made with aggregated Co(OH)₂ with a d50 of 19.1 μm andLi₂CO₃ with a Li to Co blending ratio of 1.07. The mixed powder is firedin air at 950° C. for 10 hours. After cooling, the obtained material ismilled and screened with a 270 mesh screen.

Physical properties and selected electrochemical results for examplesand comparative examples are listed in Table 1. Even though different Lito Co ratios and temperatures are used for the Examples 1 to 3, the d50of the particles are about the same, in the range of 17.0 to 17.4 μm.This large particle size is reflected by the low BET, which is 0.17 m²/gor below. With such a large particle size, all three examples give highpress density, around 3.77 g/cm³. Regarding chemical composition, theyhave a Li to Co ratio of almost one. Their OH⁻ contents are in the rangeof 0.012 to 0.014 wt %. They have excellent discharge capacity at 2 Crate, as well as excellent rate capability.

In Comparative Example 1, Co₃O₄ is used as a precursor. The obtainedLiCoO₂ has a smaller d50 than in Example 2, where Co(OH)₂ was used, eventhough a higher Li to Co ratio was chosen in the blend. This results ina high Li-excess in the final product. This excess penalizes the ratecapability, which is poor compared to Example 2, even though theparticle size is slightly smaller. Probably due to its wider particlesize distribution, the product has a slightly higher press density.

The powder according to Comparative Example 2 is made at a relativelyhigh temperature, but at a low blending ratio. The obtained powdertherefore has a significant Li deficit. Its OH⁻ content is only 0.008 wt%. In this case, there is Co₃O₄ present as an impurity in the product.This is clearly shown in FIG. 3, where the product according to Example1 is shown for reference.

The powder of Comparative Example 3 is prepared starting from the sameCo(OH)₂ precursor as in Examples 1 to 3, but with a lower Li to Co ratioand a lower firing temperature. The product still has d50 of 17 μm,which is just slightly smaller than the 19.3 of the Co(OH)₂. However,this product has a low press density of only 3.52 g/cm³, because of itssmall primary particles and ensuing high BET of 0.45 m²/g. This exampledemonstrates that a large primary particle size is needed to obtain ahigh density LiCoO₂.

The powder of Comparative Example 4 is prepared starting from Co(OH)₂precursor with badly formed secondary particles. Even it is blended andfired in the same conditions as Example 2, it has a d50 of only 9.8 μmand a low press density of 3.63 g/cm³. To make high density materialwith such a precursor having a small secondary particle size, a high Lito Co blending ratio is needed. This is not recommended because the soobtained LiCoO₂ will end up with a too high Li excess. Therefore, tomake LiCoO₂ with a large primary particle size, Co(OH)₂ with largesecondary particle size is needed.

TABLE 1 Precursor Blend Product d50 Li to Co Firing Li to Co OH⁻ d50 BETDensity Q2C Rate Type (μm) (at./at.) (° C.) (at./at.) (wt %) (μm) (m²/g)(g/cm³) (mAh/g) (%) Ex. 1 Co(OH)₂ 19.3 1.05 980 0.998 0.013 17.4 0.153.76 147.4 91.8 Ex. 2 Co(OH)₂ 19.3 1.05 970 0.999 0.014 17.0 0.17 3.75147.8 92.2 Ex. 3 Co(OH)₂ 19.3 1.04 990 0.984 0.012 17.4 0.14 3.79 146.291.2 Comp Co₃O₄ 3 1.065 960 1.016 0.018 13.9 0.19 3.79 141.0 88.9 Ex. 1Comp Co(OH)₂ 19.3 1.035 1020 0.963 0.008 17.8 0.16 3.76 141.7 89.9 Ex. 2Comp Co(OH)₂ 19.3 1.005 920 17 0.45 3.52 Ex. 3 Comp Co(OH)₂ 9 1.06 9609.8 3.63 Ex. 4 Comp Co(OH)₂ 19.3 1.06 960 1.019 0.021 18.2 0.16 3.78142.8 89.9 Ex. 6 Comp Co(OH)₂ 19.1 1.07 950 1.025 0.041 23.2 0.13 3.78140.6 89.2 Ex. 7

Table 2 lists results related to Mg-doped products. The productaccording to Example 4 has about the same density as the productaccording to Comparative Example 5. With a Li to Co-plus-Mg ratio closeto 1.0, Example 4 boasts a higher capacity and a better rate capabilitythan Comparative Example 5.

TABLE 2 Product Precursor Blend Li to d50 Li to Co Firing (Co + Mg) d50BET Density Q2C Rate Type (μm) (at./at.) (° C.) (at./at.) (μm) (m²/g)(g/cm³) (mAh/g) (%) Ex. 4 Co(OH)₂ 18.7 1.05 980 0.996 20.1 0.18 3.79137.2 87.5 Co/Mg = 99 Comp Co₃O₄ 3 1.057 980 1.017 17.3 0.16 3.78 134.886.8 Ex. 5 Co/Mg = 99

Example 5 is the result of mixing powder from Example 4 with 20% ofLiCoO2 with a smaller d50. Press density increases from 3.79 g/cm³ to3.83 g/cm³.

In Table 3 the process characteristics are investigated. In fact, toobtain the stoichiometric high density LiCoO₂ according to theinvention, the correct combination of blending ratio R (=Li/Co) andfiring temperature T should be respected, as listed in the followingtable.

TABLE 3 R vs T diagram R T 1.04 1.045 1.05 1.055 1.06 960 ✓ Over OverOver 970 ✓ ✓ ✓ Over Over 980 ✓ ✓ ✓ ✓ Over 990 ✓ ✓ ✓ ✓ ✓ 1000 Under ✓ ✓ ✓✓ 1010 Under Under ✓ ✓ 1020 Under Under Under ✓

In the table, “Over” means that an excess of Li is used for a firingtemperature that is too low. On the contrary, “Under” stands for firingat a temperature which is too high for the given Li/Co ratio. For “√”the correct conditions are used.

1-13. (canceled)
 14. A lithium cobalt oxide powder for use as an activepositive electrode material in lithium-ion batteries, having a d50 ofmore than 15 μm, a specific surface area (BET) of less than 0.2 m²/g,and a Li to Co atomic ratio between 0.980 and 1.010.
 15. The lithiumcobalt oxide powder of claim 14, having an OH⁻ content between 0.010 and0.015 wt %.
 16. The lithium cobalt oxide powder of claim 14, furthercomprising Mg as a doping element, having a Mg to Co atomic ratiobetween 0.001 and 0.05, and having a Li to the sum of Co and Mg atomicratio between 0.980 and 1.010.
 17. A powder mixture for use as an activepositive electrode material in lithium-ion batteries, comprising atleast 50% by weight of a first powder, wherein the first powder is thelithium cobalt oxide powder of claim 14, and a second powderous activecomponent consisting of a lithium transition-metal oxide.
 18. The powdermixture of claim 17, wherein the medium particle size of the secondpowderous active component is smaller than that of the first powder, andwherein the particle size distribution of the powder mixture is multimodal.
 19. The powder mixture of claim 18, wherein the second powderousactive component consists of lithium cobalt oxide, the mixture having aBET of less than 0.5 m²/g.
 20. A precursor compound of the powder ofclaim 14, consisting of either one or more of powderous non-sinteredagglomerated cobalt oxide, hydroxide and oxy-hydroxide, and having asecondary particle size with a d50 of more than 15 μm.
 21. The precursorcompound of claim 20, whereby the secondary particles are essentiallyspherical.
 22. An electrode mix comprising the powder of claim 14 as anactive material.
 23. A lithium-ion battery comprising the electrode mixof claim
 22. 24. A single firing process for manufacturing the lithiumcobalt oxide powder of claim 14, comprising: providing the precursorcompound of claim 20, mixing said precursor compound with a Li sourceaccording to a Li to Co ratio R between 1.04 and 1.06 to obtain amixture, and firing said mixture with a single firing at a temperature Tbetween 960° C. and 1020° C., whereby the quotient Q of the firingtemperature T and the Li to Co ratio R corresponds to 920≦Q≦965.
 25. Thesingle firing process of claim 24, wherein 1.04≦R≦1.05 and 92023 Q≦960.26. The single firing process of claim 24, wherein 1.05≦R≦1.06 and925≦Q≦965.
 27. The lithium cobalt oxide powder of claim 15, furthercomprising Mg as a doping element, having a Mg to Co atomic ratiobetween 0.001 and 0.05, and having a Li to the sum of Co and Mg atomicratio between 0.980 and 1.010.
 28. A powder mixture for use as an activepositive electrode material in lithium-ion batteries, comprising atleast 50% by weight of a first powder, wherein the first powder is thelithium cobalt oxide powder of claim 15, and a second powderous activecomponent consisting of a lithium transition-metal oxide.